﻿1851.] MURCH1SON SILURIAN ROCKS OF SCOTLAND. 139 



the tract around it, we subsequently travelled through Wigtonshire, 

 Galloway, and Kircudbright, and lastly made transverse sections 

 across the central ridge in Dumfriesshire, the country which Mr. Hark- 

 ness has recently described*. 



In offering the following observations, no one can be more impressed 

 than myself with the difficulty which must for some time prevail 

 in producing a detailed monograph of the Silurian Rocks of Scot- 

 land. Their numberless dislocations and contortions would be diffi- 

 cult to unravel, even in a clearly exposed mountain-chain ; but when 

 we add to this, that, for the most part, the strata are obscured by 

 vegetation, bogs, or drift, and also broken througli by a variety of 

 igneous rocks, every one will perceive that the task of placing them 

 in their original order of succession is one which can only be ac- 

 complished by long-continued and close labour, such as has cha- 

 racterized the Geological Survey of England and Wales. This effort 

 in physical geology might indeed, I am persuaded, be accomplished 

 by persons like Professor Nicol and those who have begun it ; but 

 I do not desire to see good geologists set to such a labour of detail 

 until the region be adequately laid down and mapped by the Govern- 

 ment Geographical Surveyors. If Scotland be not freed from the dis- 

 grace of being almost the only country in Europe whose surface is not 

 yet correctly mapped, it is vain that we can look for sound geological 

 details, In the absence of such geographical data, the working geo- 

 logist is discouraged in his first efforts to reform the maps hitherto 

 produced, the chief one of which, usually known as MacCulloch's map, 

 is so replete with errata, that although it would be a waste of time to 

 attempt to enumerate them all, a certain number of them are subjoined 

 in a footnote f. 



* Quart. Journ. Geol. Soc. vol. vii. pp. 46 et seq. 



t The following errata, chiefly drawn up by Professor Nicol, may be taken as 

 samples of the defects of MacCulloch's Geological Map, and, although some of 

 them have been remedied in more recent maps of the British Isles, very much 

 remains to be done in correcting outline mistakes and erroneous classification. 



In the south-east the sandstones of Roxburgh and Berwick are coloured as Red 

 Sandstone, whereas a large part of them belong to the carboniferous or mountain 

 limestone. This is also true of the same formation on the coast south of Dunbar, on 

 the other side of the southern Silurian axis. The limits of these sandstones and 

 of the other formations are in both places very inaccurate, and more especially in 

 the upper part of Liddesdale. A great part of the trap-rocks in the sandstones is 

 omitted. The igneous eruptions in the Silurian rocks are almost entirely passed 

 over. Not a single trap-dyke is laid down, although some run continuously for many 

 miles — one at least for nearly thirty. Whole hills of felspar-porphyry and syenite 

 are coloured as clay-slate — as the promontory of St. Abb's Head, Cockburn Law, 

 Priestlaw (the Fassney granite of Playfair), Derrington Law in Berwickshire, 

 Wendestraw Law in Peebles, and Selkirk, with many others of less note, well 

 known to Professor Nicol. 



In the south-west all the granite and trap near the Mull of Galloway are omitted, 

 and also the important trap-rocks and serpentines of Bennan Head, &c, and 

 all the igneous rocks described in this memoir. The Silurian rocks N. of Girvan 

 are laid down as Old Red Sandstone. 



In the centre of Scotland no dependence can be put on what is coloured as 

 Red Sandstone, or on what is laid down as Coal. The trap rocks are also very 

 imperfectly delineated. In the Pentland Hills, for instance, many square miles 

 coloured as trap are Silurian sandstone. Of the latter not a trace is seen in 



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